Mapping Prior Beta Grains in Ti 6Al 4V after Additive Manufacturing and Post Processing

It is well established that additively manufactured (AM) Ti 6Al 4V grows from the melt with cubic beta grains building epitaxially on the underlying beta grains with a cube texture aligned with the build direction. On cooling the beta structure largely transforms to a hexagonal alpha phase with 12 possible crystallographic variants. This complexity makes mathematical beta reconstruction challenging.

The residual beta phase that is retained after cool down can be identified by EBSD within an alpha plus beta map. If the alpha-identified pixels are discarded, then the beta-identified pixels can be electronically grown to fill space. Similarly oriented beta grains will merge into one orientation and the net result is a map of the prior beta structure. With these maps, all crystallographic manipulations available within the EBSD software can be made.

Here, reconstruction of the prior beta structure is demonstrated for samples of AM Ti 6Al 4V that have been post processed and deformed in tension in three orthogonal directions relative to the build direction. The change in beta morphology after differing post build hot isostatic pressing (HIP) is demonstrated. Prior-beta texture is mapped and related to tensile properties measured in mutually orthogonal orientation.